The Selectors (16-bit) sensor has detected a high level of selector usage. Selectors are used in the memory management for 16-bit applications. There is a total of 8192 selectors available under Windows, but some applications use hundreds of selectors. When no selectors are available, out of memory errors result, and you cannot open more 16-bit applications.
To make more selectors available, close any non-essential 16-bit applications.
If the problem persists, consider upgrading to 32-bit versions of your 16-bit applications. To distinguish 16- from 32-bit applications, open System Information and click Details on the Memory tab.
The trigger level for this sensor's alarm determines what Norton System Doctor considers a "high" level of selector usage. To change the trigger level, click Change Alarm Settings.
